One electrophotographic type image forming device conventionally well known in the art includes a developing unit. One such developing unit is mounted in the image forming device so that a developing roller provided in the developing unit contacts a photosensitive drum provided in the image forming device.
As the developing unit, an image forming cartridge including a cartridge casing and a developing roller has been proposed. The cartridge casing is formed in a generally box shape having a front wall provided with two foot portions at respective widthwise ends and a top wall provided with a pressing operation mechanism. The developing roller is accommodated in the cartridge casing.
When the above image forming cartridge is mounted in the image forming device, a pressure force generated by the pressing operation mechanism urges the image forming cartridge downward. A component of the pressure force brings each foot portion into contact with a guide member, such as a roller, provided at the image forming device. In association therewith, the developing roller is brought into contact with the photosensitive drum. As a result, the image forming cartridge is subjected to positioning relative to the image forming device.